(a) Field of the Invention
The present invention relates to an epoxy resin composition for sealing photosemiconductor elements which is excellent in transparency and reliability and useful in sealing photosemiconductor devices, and to a photosemiconductor device sealed with the epoxy resin composition.
(b) Description of the Related Art
Photosemiconductor elements, such as light-emitting elements and photo receptors, have been sealed mainly with transparent epoxy resins containing acid anhydride hardeners and amine cure accelerators, because of the necessity for transparency.
The use of acid anhydrides as hardeners has required dampproofing with the greatest circumspection since acid anhydrides are easily hydrolyzed by water to cause deterioration in their properties. Also the cured products essentially have a shortcoming of poor moisture resistance due to the ester bonds made by the reaction of the acid anhydrides with epoxy resins. Further, the molded products are hardly satisfactory both in adhesion to metal and in thermal shock resistance.
To solve the above-described problems, it has been proposed to use specific phenol novolac resins as hardeners (Japanese Patent Application Unexamined Publication No. 6-184281). This proposal has shown that phenol novolac resins are less influenced by the presence of water than acid anhydrides, and the resulting cured products are somewhat improved in moisture resistance, thermal shock resistance and adhesion. As to transparency (light transmission factor) which is the most important property of the sealing materials for photosemiconductors, the cured products, however, are occasionally clouded due to the severe coloration of the phenol novolac resins by heat or due to their poor compatibility with epoxy resins, so that the cured products cannot satisfy the transparency standard required of packages of photosemiconductors and cannot receive practical application.